Optically and electrically programmable silicided polysilicon fuse device

ABSTRACT

A silicided polysilicon based fuse device that is programmable by optical and electrical energy in the polysilicon layer without damage to nearby structures, comprising:  
     a Si substrate;  
     an insulating layer disposed on the substrate; and  
     a fuse device section comprising poly-Si/a silicide/ and a barrier layer, the fuse device section forming an electrical discontinuity in the poly Si layer in response to an electrical pulse or an optical pulse applied to it.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The invention relates to integrated circuit devices, and moreparticularly, to fusible link devices in semiconductor integratedcircuits in which the laser fuse is made in the poly-Si level, asopposed to the metal level, which can be placed in oxide.

[0003] 2. The Prior Art

[0004] In general, today, integrated circuits are made with internalconnections that are set during manufacturing; however, due to highdevelopment costs, lengthy lead times, and the high tooling costs ofthese circuits, the end user prefers circuits which can be programmed inthe field. These circuits are typically referred to as programmablecircuits since they usually contain programmable links.

[0005] Programmable links are electrical interconnects which are brokenor created at selected electronic nodes by the end user after theintegrated circuit device has been fabricated in order to activate ordeactivate the selected electronic nodes.

[0006] As a case in point, programmable links are used widely inprogrammable read-only memory devices (PROMs). In this connection, it ispointed out that the most common form of programmable link is thefusible link. Upon obtaining a PROM device, typically it will consist ofan X-Y lattice of conductors or semiconductors. The lattice comprises acrossover point of a conducting link, which is referred to as a fusiblelink, that connects a transistor to this lattice network. To program thePROM, the fusible link is blown at selected nodes to create an opencircuit. The combination of blown and unblown links constitutes adigital bit pattern of ones and zeros that constitute data which theuser stores in the PROM.

[0007] Some of the key disadvantages of fusible link PROM systems isthat, because of the nature of the conducting material in the link, highvoltage and high current levels are usually needed during programming inorder to complete blowing of the fusible link. Because the link isrelatively high in conductance, it requires a considerable amount ofpower dissipation to blow it. Further, the size and shape of the fusiblelink must be exacting so that the link will function effectively as aconductor if it is not blown and be a completely open circuit if it isblown.

[0008] A second type of programmable link has also been utilizedfrequently. The second type of programmable link is referred to as ananti-fuse link, and enjoys considerable use in integrated circuitapplications. In the anti-fuse link, instead of the programmingmechanism causing an open circuit as is the case with fusible links, theprogramming mechanism creates a short circuit or low resistance link.The anti-fuse link consists of two conductor and/or semiconductormaterials with a dielectric or insulating material between them. Duringprogramming, the insulating or dielectric material at selected points inbetween the conductive material is broken down by a predeterminedapplied voltage to electrically connect the conducting or semiconductingmaterials together.

[0009] A silicide agglomeration fuse device is disclosed in U.S. Pat.No. 5,708,291. The fusible link device is disposed on a semiconductorsubstrate and comprises:

[0010] a polysilicon layer having a first resistance;

[0011] a silicide layer formed on the polysilicon layer, the silicidelayer having a second resistance lower than the first resistance, thesilicide layer agglomerating to form an electrical discontinuity inresponse to a predetermined programming potential being applied acrosssuch that the resistance of the fusible link device can be selectivelyincreased and;

[0012] nine contacts electrically coupled to either end of the silicidelayer for receiving the programming potential.

[0013] U.S. Pat. No. 5,969,404 disclose a fusible link device on asemiconductor substrate for providing discretionary electricalconnections. The fusible link device has a first un-programmedresistance and includes a polysilicon layer and a silicide layer. Thesilicide layer is formed on the polysilicon layer, and agglomerates toform an electrical discontinuity in response to a predeterminedprogramming potential being applied across the silicide layer, such thatthe resistance of the fusible link device can be selectively increasedto a second programmed resistance.

[0014] A polysilicon fuse array structure for integrated circuits isdisclosed in U.S. Pat. No. 5,536,968. The semiconductor structurecomprises:

[0015] a first electrical conductor;

[0016] a second electrical conductor electrically separated from thefirst electrical conductor;

[0017] a polysilicon strip connecting the first and second electricalconductors and forming a fuse between the first and second electricalconductors, the polysilicon strip including a narrow middle section,whereby the fuse will be opened by a current which is passed from thefirst electrical conductor through the polysilicon strip into the secondelectrical conductor;

[0018] a first patterned signal layer, the first electrical conductorand the polysilicon strip residing in the first patterned signal layer;and

[0019] a second patterned signal layer electrically separated from thefirst patterned signal layer, the second electrical conductor residingin the second patterned signal layer.

[0020] U.S. Pat. No. 6,104,079 disclose closely pitched polysiliconfuses and a method for making the same. In the method for decreasing thepitch of polysilicon fuses tungsten barriers are formed adjacent to thefuse elements and the tungsten barriers are made compatible with theprocess to form a crack stop. The tungsten is stacked at the via levelon top of the tungsten at the contact level in the crack stop, and theinterlevel dielectric is used as a cover for the fuse. In this way, thetungsten fuse barrier process is made compatible with the polysiliconfuse crack stop process.

[0021] An electrically global fuse in a reduced co-sectional area isdisclosed in U.S. Pat. No. 6,222,244 B1. The semiconductor fuse ispositioned between conductors for connecting at least two wiring lines.The fuse comprises spacers positioned on adjacent one's of theconductors, and the fuse element is positioned between the spacers andconnected to the wiring lines. A space between the conductors comprisesthe first width comprising a smallest possible photolithographic widthand the fuse element has a second width smaller than the first width.This fuse protects the semiconductor device from excessive voltageand/or current or selectively and permanently connect/disconnectsemiconductor devices from one another.

[0022] U.S. Pat. No. 5,266,829 disclose an electrically programmablelow-impedance, anti-fuse element. It consists of a capacitor-likestructure having a first electrode and a second electrode with adielectric layer in between, characterized by a high impedance and verylow leakage current before programming and a low-resistance afterprogramming. A plurality of these anti-fuses is disposed in asemiconductor integrated circuit, and maybe selectively blown to createlow impedance interconnects at selected locations within the integratedcircuit. The anti-fuses may be blown either before or after packaging ofthe integrated circuit die.

[0023] U.S. Pat. No. 5,882,998 disclose a low power programmable fusestructure and method of making the same.

[0024] The method comprises:

[0025] providing a substrate having a filed oxide region;

[0026] forming a mask over the doped polysilicon strip such that awindow exposing the doped polysilicon strip is defined at about thecenter of the doped polysilicon strip;

[0027] applying an increased implant dose over the mask and the exposeddoped polysilicon strip lying within the window to produce an increaseddopant concentration region in the doped polysilicon strip, theincreased implant dose being between about 3.10¹⁵ cm⁻² and about 6×10¹⁵atoms cm⁻²; and

[0028] forming a silicide metal over the doped polysilicon strip suchthat a thinner layer of the silicide metal is formed over the increaseddopant concentration region and a thicker layer of the silicide metal isformed over other regions of the doped polysilicon strip.

[0029] There is a need in the art of utilizing programmable fuses inintegrated circuits to reduce the damage to SILK by other than thecurrent method of using fuses in the final metal level which may beplaced in oxide, and wherein some damage to the structure still results.

[0030] There is a further need in the art of providing programmable fuselinks for use in integrated circuits to alleviate physical damage to thestructure, as is typically the case when the fuses are electricallyprogrammed.

[0031] There is a further need in the art of providing programmablefuses for use in integrated circuits to be able to utilize less energywhen compared to ablation or melting, and to reduce the pitch and damageto nearby structures.

[0032] Finally, there is a need in the art of providing programmablefuses for use in integrated circuits to eliminate refractory metals thatare normally needed as liners for poly-Si lines, to be able to useshorter wavelengths, and thereby tighter focal spots that lead toreduced pitch, but which also lends itself to being electricallyprogrammed (and thereby provide the improved flexibility of affectingprogramming with either optical energy or electrical energy).

SUMMARY OF THE INVENTION

[0033] One object of the present invention is to provide programmablefuses in integrated circuits that reduce the damage to interleveldielectrics and neighboring structures by avoiding using fuses in thefinal metal level (which may be placed in oxide), and where some damageto the structure still occurs.

[0034] Another object of the present invention is to provideprogrammable fuse links for use in integrated circuits that, unlike allcurrently known methods of programming, are free from physical damage tothe structure.

[0035] A further object of the present invention is to provideprogrammable fuses for use in integrated circuits that utilize lessenergy in comparison to ablation or melting techniques, and that reducesthe pitch and damage to nearby structures upon programming.

[0036] A yet further object of the present invention is to provideprogrammable fuses for use in integrated circuits that are capable ofbeing programmed by optical means, of shorter wavelengths, and therebyreducing the focal spot size of the itself to being electricallyprogrammed as well as optically optical beam that lead to reduced pitch,but which also lends programmed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0037]FIG. 1 is a microphotograph of a fuse link of the prior art inwhich there are metal lines on oxide/low dielectric constant materials,and in which there is a splatter.

[0038]FIG. 2 is a microphotograph of a fuse link of the prior art inwhich there is a metal line on oxide/low-dielectric constant materials,and in which there is a crack.

[0039]FIG. 3 is a microphotograph of the silicided polysilicon basedfuse of the invention after programming.

[0040]FIG. 4 shows a top view of a microphotograph of a fusible linkdevice of the present invention comprising a large array structure of aneFuse bank in which silicided poly-Si lines are programmed by athick-oxide.

[0041]FIG. 5 shows a top view of a microphotograph of a single fusiblelink device of the present invention comprising an eFuse in whichsilicided Poly-Si lines are programmed by a thick-oxide.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0042] Reference is now made to FIG. 1 which shows a microphotograph ofa fuse link, wherein metal lines on oxide/low dielectric constantmaterials evidence a splatter formed by the high energy needed toprogram this fuse. When programming similar fuse links found in theprior art, a large pitch is needed and this is another disadvantageattendant to the use of this fuse link. Further disadvantages associatedwith the large pitch that is needed for programming in the prior artfuse link is the damage caused to the layers beneath the fuse, and thatthe fuses are isolated in a fuse box (and this causes an area penalty).Additionally, there are complications in back-end integration—such asflip chip bonding—when utilizing this prior art poly-Si based fuse link.

[0043] A still further disadvantage in addition to the splatter createdfrom high energy when programming the prior art fuse link is that cracks11 are created upon programming, as can be seen in the microphotographof FIG. 2.

[0044] The invention silicided polysilicon based fuse device that may beprogrammed either optically or electrically is shown in FIG. 3. In thisfigure, which comprises a top view as well as a cross sectional sideview of the silicided polysilicon based fuse device, there is a siliconsubstrate 20 with an insulating layer 21 disposed above. In thisembodiment of the fuse device, the fuse device section FDS is disposedon the insulating layer 21, as a part of a larger integrated circuitdevice. The polysilicon layer 22 may be doped p-type; however, otherembodiments or configurations may include other types of dopingincluding n-type or the formation of p-n junctions in the polysiliconlayer 22. The fuse device section FDS includes a Cobalt silicide (CoSi₂)layer 23 disposed on the polysilicon layer 22, and a transparentpassivation layer 24 on the CoSi₂ layer 23. In operation, the fusedevice section FDS is characterized by a resistance in the silicidedpolysilicon before it is programmed or blown. As may be seen from FIG.3, in the programmed state, the higher resistance is obtained because ofthe removal of the CoSi₂ in some regions. It is apparent that the fuselink has not been physically ruptured in order to achieve this higherresistance state. Furthermore, the passivation layer 24 is unperturbedduring the entire process.

[0045] It is believed that any dopants in the polysilicon that maycontribute to any residual conduction have also rendered inactive due toprogramming. The SiN layer functions as an encapsulation or barrierlayer, which while allowing the transmission of optical energy, allowsfor the change in the resistance of the silicided polysilicon layerwithout rupturing this layer.

[0046] In the context of the invention, while CoSi₂ is preferred as thesilicide, other silicides such as titanium, tungsten, or platinumsilicides are equally operable. Also, in the context of the inventionthe SiN is the preferred encapsultation layer; however, any transparent,encapsulation or barrier layer will suffice.

[0047]FIG. 4 shows a microphotograph of the present invention structurecomprising a large array of fuse links, showing silicided poly-Si linksthat are programmed. Preferably, the programming in this embodiment isdone at about 3.3V and about 10 mA for about 200 microseconds, whereuponcurrent is caused to flow between contacts 30 as shown in FIG. 5. Thecurrent flows through the fuse link to affect a change in the resistanceof the fuse link, without rupturing the link 31. In other words, thebasic resistivity fuse link is changed. The silicided polysilicon basedfuse device of the invention may be programmed by the application ofoptical energy in the visible and NIR (near infrared) range realizingthe increased local resistivity, again without any rupture. Further,there is no absorption in the inter-level dielectrics, oxide andnitride.

[0048] The novel irnventive structure removes the disadvantages ofmetal-link laser fuses, provides flexibility in product choice and testflow, and allows programming by either laser or electrical means, and inso doing, induces a large resistance change in excess of 10⁵ Ohms,without rupture of the link.

I claim:
 1. A silicided polysilicon based fuse device that isprogrammable by optical and electrical energy in the polysilicon layerwithout damage to nearby structures, comprising: a Si substrate; aninsulating layer disposed on said substrate; a fuse device sectioncomprising poly Si/a silicide/and a barrier layer, said fuse devicesection showing a local increase in its resistance due to theapplication of an electrical pulse applied across it or by theapplication of an optical beam over it.
 2. The silicided Poly siliconbased fuse device of claim 1 wherein said barrier layer is SiN.
 3. Thesilicided Poly silicon based fuse device of claim 1 wherein saidinsulating layer silicon dioxide.
 4. The silicided Poly silicon basedfuse device of claim 3 wherein said insulating layer is silicon nitride.5. The silicided Poly silicon based fuse device of claim 1 wherein saidsilicide is selected from the group consisting of cobalt silicide,titanium silicide, tantalum silicide and platinum silicide.
 6. Thesilicided poly silicon based fuse device of claim 3, wherein saidsilicide is cobalt silicide.
 7. The silicided Poly silicon based fusedevice of claim 3 wherein said silicide is titanium silicide.
 8. Thesilicided Poly silicon based fuse device of claim 3 wherein saidsilicide is tungsten silicide.
 9. The silicided Poly silicon based fusedevice of claim 3, wherein said silicide is tantalum silicide.
 10. Thesilicided Poly silicon based fuse device of claim 3, wherein saidsilicide is platinum silicide.
 11. The silicided Poly silicon based fusedevice of claim 2, wherein said silicide is selected from the groupconsisting of cobalt silicide, titanium silicide, tungsten silicide,titanium silicide and platinum silicide.
 12. The silicided Poly siliconbased fuse device of claim 11, wherein said silicide is cobalt silicide.13. The silicided Poly silicon based fuse device of claim 11, whereinsaid silicide is titanium silicide.
 14. The silicided Poly silicon basedfuse device of claim 11, wherein said silicide is tungsten silicide. 15.The silicided Poly silicon based fuse device of claim 11, wherein saidsilicide is tantalum silicide.
 16. The silicided Poly silicon based fusedevice of claim 11, wherein said silicide is platinum silicide
 17. Thesilicided Poly silicon based fuse device of claim 11, wherein theprogramming potential is about 3.3V.
 18. The silicided Poly siliconbased fuse device of claim 11, wherein the programming is by an opticalbeam.